Coatings for tablets for human or animal consumption (as for other uses) may be applied with a system consisting of a rotating horizontal-axis drum for tumbling the tablets while a coating substance is sprayed within the drum. Typically, the drum is perforated to permit a flow of heated air through the drum wall to facilitate drying. As well, perforations permit cleaning fluid to readily drain. Such perforations may take on a variety of shapes and sizes suitable to the desired application. Tablet coating systems are used in a variety of other applications, for example in pharmaceuticals and for coating of candies. As well, such systems may be used for coating seeds. Tablets are typically produced in a wide range of shapes, sizes and densities. Accordingly, any system for coating the tablets or the like should be capable of efficient coating of a range of tablet types. A typical such system includes a housing, a horizontal-axis perforated drum journaled for rotation within the housing, drive means for rotating the drum, for example an electric motor which may be external to the housing and operatively connected to the drum, for example by a belt or chain drive, means for introducing uncoated tablets into the drum and for removing the coated tablets following the coated process.
Such a system requires a means for spraying or otherwise introducing a coating such a liquid coating solution into the drum. For pharmaceutical use a high level of precision in the coating process is required in order to maintain a controlled thickness and weight of coating. Preferably, the system includes a means for introducing a flow of air through the drum wall, for example heated air to facilitate the drying process. Finally, the system should permit thorough washing of components which are in contact with the tablets and spray liquid. Washing of the equipment may be provided by means of fully or semi-automatic systems or a fully-manual approach.
Tablet coating systems are described in U.S. Pat. No. 4,725,446 to Forster et al., which describes a rotateable horizontal axis drum having a perforated wall. A supply of drying air flows through the wall. Coating solution is sprayed onto the tumbling tablets via a sprayer centrally positioned within the drum directed generally downwardly towards the tumbling bed of pills within the drum interior.
Prior art systems generally provide for batch processing of tablets, which is relatively inefficient in comparison with a continuous industrial process. However, batch processing generally requires simpler equipment, particularly in the pharmaceutical processing context in which a high level of precision is required in supplying a selected amount of coating for a given batch size of tablets as well as tablet dwell time within the drum. Thus, it is relatively simple to introduce a carefully measured batch size of tablets into the drum and thereupon apply a measured amount of coating to the tablets. Continuous processing, while more efficient, introduces difficulties in terms of consistency of the coating process.
Another aspect of coating systems, particularly in the pharmaceutical industry, relates to rinsing and washing of the equipment, particularly those components in contact with the product. A high standard of cleanliness applies to the equipment, in particular when the machine is switched from one product to another. It is desirable to provide a convenient system for spraying a cleaning solution throughout the drum interior, with minimal worker contact with the equipment.